This study examines the effects of a progessive physical conditioning program (walking, running, jogging) on a group of 48 initially sedentary men aged 35-55, in comparison with a control group of 32 similar men who are not exercising. Initial allocation to exercise or control was random. Measurements of plasma lipoprotein concentrations, percent body fat, weight, exercise electrocardiogram, maximum oxygen uptake, 3-day diet record and various other physiological and psychological measures have been determined on exercisers and controls at baseline (2 measures), and after 3 months, 6 months, 9 months, and 1-year of exercise or sedentary life. At this point all participants have completed one year of the study. The exercisers as a group have clearly increased their maximum oxygen uptake compared to the controls (unchanged), and weight loss was greater in the exercisers. The influence of the exercise upon plasma lipoprotein pattern (measured as lipoprotein cholesterol concentration, analytical ultracentrifuge pattern and concentration of apolipoprotein AI and AII) is currently being assessed after 1-year of exercise, and at intermediate points. Suitable adjustments will be made for changes in body weight and dietary intake occurring during the year. In this way it is anticipated that the long-term sequence of changes in plasma lipoproteins and their subfractions occurring as individuals become fit can be elucidated, in comparison with a sedentary control group. The second year of this project will be devoted to analysis of the 1-year results, and extension of the study to two years for those exercisers electing to continue training at a high level for an additional year.